Server Sent Events Not Working

export function startAiSSE(
  userMessage: string,
  onChunk: (chunk: string) => void,
  onClose: () => void,
  onError: (err: any) => void
) {
  const url = `http://localhost:3001/test`;

  fetchEventSource(url, {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify({
      userMessage: userMessage,
    }),
    onmessage(ev) {
      console.log("RAW DATA RECEIVED ON CLIENT:", ev.data);
      try {
        const parsedData = JSON.parse(ev.data);

        if (parsedData.event === 'response.content_part.delta' || parsedData.event === 'response.content_part.done') {

          const textChunk = parsedData.data?.part?.text || '';

          if (textChunk) {
            onChunk(textChunk);
          }
        }
      } catch (e) {
        console.error('Failed to parse SSE message data:', ev.data, e);
      }
    },
    onclose() {
      console.log('SSE connection closed.');
      onClose();
    },
    onerror(err) {
      console.error('SSE Error:', err);
      onError(err);
      throw err;
    },
  });
}